前陣子，有一位網(wǎng)友提及 SAS 中有 monotonic() 這么一個(gè)未記錄在軟件手冊(cè)中的函數(shù)1。其實(shí)除了函數(shù)之外，SAS 中有更多的未記錄過程步。比如早期的實(shí)現(xiàn)多線程排序的 proc sortt、用來檢查單詞拼寫的 proc spell、用編程的方式編輯數(shù)據(jù)集中數(shù)據(jù)的 proc editor、用編程的方式編輯 DMS 環(huán)境的工具條的 proc toolbar 等等。這些過程步的相關(guān)說明已經(jīng)消失在了軟件手冊(cè)中，你僅能在網(wǎng)絡(luò)上找到零星的記錄，但如果你嘗試提交相關(guān)的命令，你會(huì)發(fā)現(xiàn)它們?nèi)匀豢捎谩?/p>

關(guān)于這些未記錄的過程步，Paul Kent (1984年加入SAS) 曾對(duì)其中一種可能做出過解釋2：

At times we've issued "the same proc with a new name" as a way of allowing us to get feedback on extensions to that procedure, without completely putting everyones production workload at risk. In the past we've seen TREPORT - new features in proc report; TFREQ - new statistics in proc freq, and SORTT - the threaded implementation... Sometimes we can prototype new features simply with new options in the existing PROC. It's usually a judgement call related to how invasive the new feature is to the structure of the production code.

We want power users to kick the tyres (for my UK friends) on some new features or implementation before they become permanent... So they remain undocumented (mostly) because the features are "transient" in the sense that they migrate into the "official" versions of the procedures, or they were not such good ideas to start with. And they remain implemented (mostly) so as not to overly in-convenience any early adopters who have been so bold as to use them in production jobs... Hope that helps y'all understand our motivation (at least a little bit)

另外有一種可能，就是隨著時(shí)代的發(fā)展，某些功能已經(jīng)"無用武之地"，例如 proc explode3。

在查找資料時(shí)，我還發(fā)現(xiàn)一個(gè)特別的例子——proc delete，它很早就被設(shè)計(jì)出來，但從 SAS 6 開始消失在了軟件手冊(cè)中，而從 SAS 9.4 開始又出現(xiàn)在了軟件手冊(cè)中，你可以通過查詢?cè)缙诘能浖謨?cè)來確認(rèn)這一點(diǎn)。它的這種行為可能是為 proc datasets 中的 delete 語句讓位，但又有過多人堅(jiān)持使用它，也可能是相關(guān)功能進(jìn)行了回爐重造4。時(shí)間久遠(yuǎn)，佐證難查，小小的變遷大概已經(jīng)成了時(shí)代的浪花。

參考：
[1]?http://www.datascientist-club.cn/forumDetail/584

[2]?http://www.notecolon.info/2010/10/what-is-proc-sortt.html

[3]?https://communities.sas.com/t5/SAS-Communities-Library/PROC-EXPLODE-The-SAS-procedure-that-time-forgot/ta-p/473102

[4]?https://blogs.sas.com/content/sasdummy/2013/07/08/proc-delete-its-not-dead-yet/